Characterization of kaolinite-3-aminopropyltriethoxysilane intercalation complexes

Earlier experimental findings of the kaolinite modified with 3-aminopropyltriethoxysilane (APTES) raised the question of the existence of more stable structures at different reaction temperatures, which has not been fully cleared up yet. Experimental and molecular simulation analyses were used to study different types of kaolinite-APTES intercalation complexes, characterizing their real structures. The displacement reactions of the kaolinite-dimethyl sulfoxide and kaolinite-urea pre-intercalation complexes were applied to synthesize the kaolinite-APTES complexes using the traditional solution/stirring method and the modern solvothermal method. The effects of the type of pre-intercalated molecules, synthesis methods, and reaction temperature (130–230 °C) on the formation of kaolinite-APTES complexes was primarily examined by X-ray diffraction (XRD), and the obtained complexes were characterized by thermal analysis, infrared spectroscopy and transmission electron microscopy. The solvothermal and solution/stirring treatments mainly produced kaolinite-APTES complexes with around 1.0-nm basal spacing. The solution/stirring treatment of the kaolinite-dimethyl sulfoxide pre-intercalation complex at 220 °C proved advantageous to form kaolinite-APTES complexes with around 1.7-nm basal spacing. In molecular dynamics simulations, these complexes with monodentate, bidentate, and tridentate APTES fixations were studied and the distributions and orientations of the grafted and free APTES molecules were predicted.